Guys,
Fuel polishing, the come to your boat with large equipment type, is really a big waste of money on a sailboat with small tankage. For a power boat with 300+ gallons it may be your only option but on a sailboat with sub 40 gallon tank I will chalk it up to a quasi scam level service.
You can DIY this job better than a professional can. Let the fuel level drop, over a period of time, suck the rest into 5 gal cans and dispose of somewhere that burns #2 oil in a furnace, boiler etc.. We're talking a few dollars worth of old fuel here.
Now spend the time and money to get in there and physically & manually scrub the tank walls. The money you save in professional polishing will pay for some excellent clean out/access ports such as those made by Seabuilt. You'll need one for each chamber in the tank. Unlike a one-time service, that really only gets the fuel in the tank clean, these access ports can be used numerous times over the life of the boat.
I have yet to see any professional "polishing" job that gets the inside of the tank "clean", not one, and I have seen a LOT of boats after they have been "professionally polished". Once you've done this job, you'll quickly see why it can't actually get the tank clean only the fuel and most of the free floating debris. The stuff is essentially like tar and no amount of pressure can reach all areas of the tank, due to baffles, or get the tank walls physically clean.
Once your tank is physically clean there is no reason not to install an on-board polishing system that, from this point onward, helps keep the tank clean and spotless.
I did this on our own boat back in 2006 and the tank walls to this day are still 100% spotless & shiny with not even a hint of discoloration. I work on far newer boats, more recently built, where the tank walls are already filthy and fuel related issues are already rearing their ugly heads.
To say that an on-board re-circulation/polishing system can't work, I can only surmise, is simply a clear lack of experience with such a system. Personally, I will never again own a vessel that runs on diesel without also having an on-board polishing system. Our re-circ system filters down to 2 micron, turns the tank twice per hour, and is completely separate from the engine system. Our fuel is always crystal clear with no-haze. The re-circ runs whenever the engine does or can be flipped on at any time even without the engine running.
Perhaps the biggest culprit I see when it comes to diesel issues is lack of o-ring maintenance on the fill cap. Ours gets replaced about every fourth fill up because it is dirt cheap and takes all of 4 seconds. Very cheap insurance. I simply located the correct size O-ring then ordered 100 of them for about $8.00.